In general, automotive passenger restraint systems perform a number of functions including acceleration sensing, signal processing and analysis, and deployment of one or more restraint devices such as frontal or side air bags and seat belt pretensioners in response to a sensed crash event. Typically, an acceleration signal is monitored to detect a potential crash event, and then filtered or integrated over the course of the crash event to produce a velocity change or .DELTA.V signal. If the .DELTA.V signal exceeds a threshold, the crash event is determined to be sufficiently severe to warrant deployment of restraints. The threshold is typically time-dependent, and is calibrated based on data logged for different types of crash events, as well as data logged during rough road driving. Multiple distributed crash sensors are sometimes used in order to obtain faster deployment decisions and to distinguish a localized crash event from a full frontal crash event. For example, the system may include a central crash sensor located in or near the passenger compartment and one or more remote sensors located near the front corners of the vehicle.
A problem with the above-described approach, with single or multiple sensors, is that it is often difficult to synchronize the time progression of the crash (that is, the event clock or timer) with the actual crash event. Various algorithms have been developed for determining if and when the event clock should be reset to improve synchronization. As a result, it can be difficult to distinguish between deployment events and non-deployment events, particularly in the first portion of the sensed event.
A related problem in systems with multiple crash sensors is that it is difficult to quickly and reliably correlate the information from the various sensors. In particular, it is difficult to reliably distinguish between a localized crash event for which deployment is desired and a localized impact (such as a deer impact or an abuse event) for which deployment is not desired.